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IVF Injections Explained: What Medications Are Used?

An IVF stimulation cycle typically involves three types of injectable medications: gonadotropins (FSH/LH) to grow multiple follicles, a GnRH antagonist or agonist to prevent premature ovulation, and a trigger shot to mature eggs before retrieval — given over 10 to 14 days on a personalized protocol based on your ovarian reserve.

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What are gonadotropins and why are they the foundation of IVF?

Gonadotropins are injectable hormones that signal the ovaries to develop multiple follicles in a single cycle. In a natural cycle your body recruits one dominant follicle; in IVF, the goal is to grow several so that more eggs are available for fertilization.

Two types are used:

  • FSH (follicle-stimulating hormone): stimulates follicle growth directly. Brand names include Gonal-F, Follistim, and Bravelle.
  • LH (luteinizing hormone): works alongside FSH to support follicle and egg development. Menopur contains both FSH and LH activity.

Dosing is individualized. Your reproductive endocrinologist will set the starting dose based on your ovarian reserve tests — typically anti-Müllerian hormone (AMH) and antral follicle count (AFC) — and adjust based on how your ovaries respond during monitoring ultrasounds 1. Current ESHRE guidance recommends personalizing gonadotropin dose to expected response based on these markers rather than applying a one-size-fits-all starting dose 2.

What prevents premature ovulation during stimulation?

Without intervention, a natural LH surge can trigger ovulation before eggs are retrieved. Two classes of medication suppress this:

GnRH agonists (e.g., Lupron / leuprolide): used in the long agonist protocol. You start this medication before stimulation begins, often in the cycle before retrieval. It initially causes a brief hormone flare before suppressing LH release.

GnRH antagonists (e.g., Cetrotide, Ganirelix): used in the antagonist protocol — now the more common choice for most patients. You add it several days into stimulation once follicles reach a threshold size. It acts quickly and wears off quickly, with no initial flare. The antagonist protocol is preferred in patients at elevated risk of ovarian hyperstimulation syndrome (OHSS) because it permits use of a GnRH agonist trigger instead of hCG 2.

Your clinic will choose a protocol based on your profile. Women with low ovarian reserve or a history of poor response often use specific variations of these approaches.

What is the trigger shot and how does it work?

Once follicles reach the target size — typically 18–20 mm — your clinic will tell you to give the trigger injection. This mimics the LH surge that causes the eggs to complete their final maturation before retrieval.

Two types are used:

  • hCG trigger (e.g., Ovidrel, Pregnyl): the traditional trigger. Highly effective but associated with a higher risk of ovarian hyperstimulation syndrome (OHSS) in high-responders.
  • GnRH agonist trigger (e.g., Lupron): only works in an antagonist protocol. Produces a shorter, more natural LH surge and significantly reduces the risk of severe OHSS for women at elevated risk 3.

Timing is precise: egg retrieval happens approximately 34–36 hours after the trigger. Missing the window matters.

Are there other medications used during an IVF cycle?

Yes — additional medications support different phases:

Progesterone supplementation: after retrieval, progesterone is given to prepare the uterine lining for embryo transfer. It is usually given vaginally (suppositories or gel) and sometimes by intramuscular injection. It continues until a pregnancy is confirmed and often through the first trimester.

Estradiol: sometimes added to support lining development, particularly in frozen embryo transfer (FET) cycles.

Antibiotics: some clinics prescribe a short course around retrieval to reduce infection risk.

Aspirin: low-dose aspirin is sometimes added to support blood flow to the uterus, though this varies by clinic and the evidence for this practice is limited.

If you have been offered pre-implantation genetic testing (PGT), the embryo biopsy happens before transfer — this does not add injections but does add a freeze-wait step.

How are the injections given and how long does stimulation last?

Most gonadotropins and antagonists are given subcutaneously — a short, thin needle into the fat of the abdomen or upper thigh. The technique is straightforward and most people manage it at home after an injection teaching session. Some clinics provide injection training videos and nursing support for questions.

Stimulation typically runs 8 to 12 days, with monitoring visits every one to two days once follicles begin growing. Blood draws (estradiol) and ultrasounds track follicle size and number so your team can adjust the dose as needed 12.

Intramuscular progesterone (if prescribed) uses a longer needle into the muscle of the outer upper buttock — some people find this more challenging and prefer the vaginal route, which is equally effective for most patients.

Common questions

Can I mix my IVF medications myself?

Some injectable formulations come ready to use in a pre-filled pen; others require mixing a powder with a diluent. Your clinic's nursing staff will walk you through the exact steps for the specific brands you are using. Never mix medications from different protocols without instruction.

What if I miss an injection?

Contact your clinic immediately. Most injection timing windows have some flexibility, but the antagonist and trigger injections in particular are time-sensitive. Your team will advise you rather than have you guess.

Do all clinics use the same IVF protocol?

No. The antagonist protocol has become common for most patients, but agonist protocols, natural cycles, and mild-stimulation IVF approaches are also used. Your reproductive endocrinologist will choose based on your ovarian reserve, age, and history.

Will Gale help me with IVF?

Gale does not directly provide fertility or reproductive endocrinology services. A board-certified reproductive endocrinologist is the specialist who performs IVF. Gale can help you prepare for appointments, organize your questions, and understand what your results mean.

Talk to a clinician

Gale can match you with a licensed clinician for a visit.

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When to contact your fertility clinic right away

  • —Severe abdominal bloating, significant weight gain (more than 2 lbs in a day), or decreased urination during stimulation — these may signal ovarian hyperstimulation syndrome (OHSS)
  • —Shortness of breath or difficulty breathing during or after stimulation
  • —Sharp one-sided pelvic pain — could indicate ovarian torsion, a rare but serious complication
  • —Signs of infection at an injection site: increasing redness, warmth, swelling, or fever

If you have severe difficulty breathing or sudden severe pelvic pain, call 911 or go to the nearest emergency room. For other urgent concerns, call your fertility clinic's after-hours line.

This article provides general health education only. It is not personalized medical advice and does not replace guidance from your reproductive endocrinologist or fertility team.

References

  1. 1.Practice Committee of the American Society for Reproductive Medicine (2021). Fertility evaluation of infertile women: a committee opinion. Fertility and Sterility. doi:10.1016/j.fertnstert.2021.08.038 ✓Framework for individualized IVF stimulation assessment including ovarian reserve testing (AMH, AFC) to guide medication dosing and monitoring
  2. 2.ESHRE Guideline Group on Ovarian Stimulation (Ata B, Bosch E, Broer S, et al.) (2026). ESHRE guideline: ovarian stimulation for IVF/ICSI: an update in 2025. Human Reproduction. doi:10.1093/humrep/deag018 ✓Evidence-based recommendations for individualized gonadotropin dosing, antagonist vs agonist protocol selection, and GnRH agonist trigger use in high-responders to reduce OHSS risk
  3. 3.Practice Committee of the American Society for Reproductive Medicine (2024). Prevention of moderate and severe ovarian hyperstimulation syndrome: a guideline. Fertility and Sterility. doi:10.1016/j.fertnstert.2023.11.013 ✓GnRH agonist trigger as preferred alternative to hCG to substantially reduce severe OHSS risk in patients at elevated risk

3 sources, numbered by first appearance. General health information, not medical advice — synthetic demonstration content.